Method for analyzing inert gas for presence of oxygen or water vapor



y 6, 1966 G. w. KElLHOLTZ ETAL 3,

METHOD FOR ANALYZING INERT GAS FOR PRESENCE OF OXYGEN OR WATER VAPOR Filed Dec. 18, 1962 SAMP COLLECTO VACUUM PUMP 11 6 k II$ wr y "VI 10 2 \13 I w 14' 15 I GAS SOURCE INVENTOR5 ATTORNEY,

United States Patent 3,262,756 METHOD FOR ANALYZING INERT GAS FOR PRESENCE OF OXYGEN 0R WATER VAPOR Gerald W. Keilholtz, Knoxville, and Curtis C. Webster,

Oak Ridge, Tenn., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 18, 1962, Ser. No. 245,952 1 Claim. (Cl. 23232) The present invention relates to a device for detecting the presence of oxygen or water vapor in any inert gas atmosphere.

In certain laboratories argon, helium and other inert gases are used in various projects and experiments. For example, these gases may be used in welding devices and in gas cooled nuclear reactors. In order to prevent undesirable oxidation and corrosion in the operation of these and other devices that use inert gases, it is desirable that no oxygen or water vapor be present in these gases. Thus, it is desirable to analyze inert gases, prior to their use, for any possible content of oxygen 'or water vapor contained therein.

Accordingly, it is a primary object of this invention to provide a device for detecting the presence of oxygen or water vapor in any inert gas atmosphere.

It is another object of this invention to provide a device which is easily fabricated and can be used repeatedly for analyzing inert gases for the presence of oxygen or water vapor.

These and other objects and advantages of this invention will become apparent upon a consideration of the following detailed specification and the accompanying drawing wherein:

The single figure illustrates one embodiment in which the principles of this invention may be carried out.

The above objects have been accomplished in the present invention by providing a transparent glass bulb in which are disposed a plurality of metallic filaments. After the glass bulb is evacuated, electrical power is supplied to one or more of the filaments in the bulb and a portion of the gas to be analyzed caused to flow into the glass bulb. If the gas in the bulb contains either oxygen or water vapor, a black coating will form over the filament when it is heated to a low temperature; subsequent heating of the filament -to a high temperature results in a white smoke being given off from the filament and deposited on the interior of the bulb, leaving the filament clean.

In the drawing, a clear glass bulb 1 is rigidly attached to a metal-to-glass seal 5 which in turn i rigidly attached to a stand plate 6 and sealed from the atmosphere. The stand plate 6 is removably attached to a gas inlet box 7 and the joint therebetween is sealed from the atmosphere by an O-ring seal, not shown. A gas inlet pipe 8 is rigidly attached to and sealed within the gas inlet box 7, and this inlet pipe 8 threadably engages with and is sealed to a pipe T 9. A plurality of metallic filaments 2 are disposed within the glass bulb 1 and are rigidly attached to metal conductors 3 which are held in place by a pacer insulator 4. The filaments 2 may be made of tungsten, for example, and the metal conductors 3 may be made of copper, for example. It should be understood that more than two filaments may be used, only two being shown for the sake of clarity in the drawing.

An electrical junction box 10 is removably attached to the gas inlet box 7. The metal conductors 3 that extend through the members 5, 6 and 7 pass through insulators (not shown) in the wall of the gas inlet box 7 and are affixed to suitable terminals within the box 10. Electrical power is furnished to one or more of the filaice ments 2, as desired, by means of a battery 11, a variable resistor 12 and a switch 13 which are connected to the appropriate terminals within the junction box 10 depending upon which desired filament or filaments are to be energized. The voltage across any filament 2 may be varied from about 10 volts to about volts depending upon which type of operation is desired as discussed below, the lower voltage being preferred to prolong the life of the filament.

The pipe T 9 is connected by means of a gas inlet line and a valve 14 to a source of inert gas 15 to be analyzed for any possible oxygen or water vapor content. A gas outlet line connects the other side of the pipe T 9 to either a vacuum pump 17 or a gas sample collector 18 by means of a two-way valve 16.

Before the gas analyzer can be used, the bulb 1 and the rest of the analyzing system (members 5, 7, 8, 9) must be evacuated to remove the air and any water vapor that might be present. vThi is accomplished by connecting the vacuum pump 17 by means of valve 16 to the interior of the analyzing system, and closing the valve 14 after gas from source 15 purges the line between the valve 14 and source 15 of any air therein. Thus any air or water vapor present in the bulb 1 and connecting lines may be removed therefrom by the vacuum pump 17. After evacuation, gas is allowed to flow through the analyzer by opening valve 14. The vacuum pump is then disconnected and the gas is directed to the collector 18 by proper operation of valve 16. If gas is allowed to flow through the line at a fast rate, then the turbulence set up by the gas passing through the T 9 will channel a portion of the gas up into the bulb 1. If the gas is allowed to fiow at a low rate, some of the gas will naturally fiow up into the bulb 1. In either event, a sufiicient sample of the gas will enter the bulb 1 o that any oxygen or water vapor present may be detected by allowing a flash of current through one of the tungsten filaments 2. It has been found that if the gas in the bulb 1 contains either oxygen or water vapor, a black coating will form over the filament when it is 'heated to a low temperature, whereas a white smoke will be detected at a high filament temperature and be deposited on the interior of the bulb 1.

It may become necessary to clean the interior of the bulb 1 after prolonged use. This may be done by detaching and removing the stand plate 6 from the gas inlet box 7. Any suitable solvent may be used for cleaning the bulb 1, for example, acetone. The provision of more than one filament is desirable in the above described device since in the event one filament should fail, the others could be used.

It has been determined that for the size filament being used when about ten volts is applied to the filament it will be heated to a dull glow, and if oxygen or water vapor are present the filament changes to a black color. Larger or smaller filaments may necessitate larger or smaller voltages, respectively, to achieve the minimum temperature for producing a dull red color. Time-color calibrations may then be used, if desired, to determine the amount of oxygen or water vapor present. If the voltage applied to a filament is raised to about 90 volts, for example, the filament is heated to nearly incandescent temperature and the presences of small quantities of oxygen or water vapor in the gas being analyzed will be indicated by the flash-oil? of white smoke from the filament.

It should be noted that when the analyzer is operated at a low voltage and if the filament acquires a black coating, this coating may be removed by momentarily increasing the voltage applied across the filament and the coating will be flashed off. The analyzer filament will then be clean and in condition for making a subsequent low voltage analysis of an inert gas ample. When the interior of the bulb becomes too cloudy with depositions of the white smoke thereon, it may be cleaned in the manner indicated above and the device reassembled for a subsequent use.

The inert gas analyzer described above may be used as a gone-go moisture gage for gases to be used in a gas-cooled nuclear reactor, if desired. Also, the analyzer may be used in certain welding operations and other applications of inert gases which require assurance that oxygen or water vapor are not present.

This invention has been described by Way of illustration rather than limitation and it should be apparent that this invention is equally applicable in fields other than those described.

What is claimed is:

A method of qualitatively analyzing an inert gas for the possible presence of oxygen or Water vapor therein comprising the steps of evacuating a transparent glass bulb containing a tungsten filament therein, flowing an inert gas sample through said bulb, connecting a first selected voltage across said filament for a short time interval to heat said filament to a dull red color, said Reterences Cited by the Examiner UNITED STATES PATENTS 1,240,700 9/1917 Friederich 313-233 X 1,859,029 5/1932 Boer et al. 313180 X 3,147,083 9/1964 Steverding et al. 23254 X OTHER REFERENCES Slowter et al.: Metal Progress, vol. 38, pp. 566 and 569 (1940).

MORRIS O. WOLK, Primary Examiner.

H. A. BIRENBAUM, Assistant Examiner. 

